This invention generally relates to cytocentrifuge sample chambers and more particularly to a novel and improved cytology chamber and method for distributing biological material on a microscope slide during the centrifugation of body fluid samples.
Cytocentrifuges are small, precision centrifuges which are particularly designed for centrifuging blood and other body fluid samples in order to separate these fluids into various components. These machines are typically used to deposit sediment materials such as cellular structures onto the surface of a microscope slide for further detailed microscopic study.
A cytocentrifuge has a removable head typically containing an even number of sample chamber assemblies in a carrier and spaced symmetrically about the centrifuge axis. The head has a removable top and an annular bowl shaped bottom. The bottom of the head supports the carrier which positions the chamber assemblies symmetrically around the inside of the annular bowl. When the top is installed on the bottom, all of the sample chamber assemblies are completely sealed inside. The assembled head is then installed in the cytocentrifuge for the centrifugal operation.
Typical cytocentrifuge or cytology chambers for centrifugation of biological fluid samples are disclosed in U.S. Pat. Nos. 4,788,154; 4,814,282; 4,391,710; 4,678,579 and 4,729,778. Each of the chambers in the latter two of these patents is actually an assembly of the chamber, a microscope slide, and a holder which includes a retaining spring bracket removably fastening the slide to the chamber and a pivot means for rotatably mounting the assembly in the carrier in the cytocentrifuge head.
A filter card may be placed between the chamber and the microscope slide for such purposes as to absorb the suspending fluid during centrifugation. Each chamber includes a funnel portion through which a fluid sample may be introduced via pipette, a sample holding portion for receiving at least a portion of the sample passing through the funnel, and a flat flange portion having a discharge opening in communication with the holding portion. The flat flange portion is designed to mate against one surface of the microscope slide. The holder is basically a channel shaped sheet metal member which receives the slide, the filter card and the flange portion of the chamber therein and has a wire spring clip which releasably holds them together in the channel. The holder also includes a bar mounted across the channel member that fits horizontally into corresponding recesses in the carrier in the bottom portion of the cytocentrifuge head so that the assembly is free to partially rotate about the horizontal axis of the bar.
The assemblies are balanced, at rest, in the centrifuge head in a tilted position such that the funnel and holding portions containing the fluid sample are inclined away from the microscope slide to keep the sample from the filter and/or microscope slide. Only during operation of the cytocentrifuge does the assembly pivot to an upright, vertical position, allowing the fluid to be centrifugally forced outward, through the discharge opening and against the filter material and/or the slide surface.
The loading of a cytocentrifuge is performed in the following manner: First, empty cytology sample chambers are assembled to a microscope slide each with a filter card between the flange member and the microscope slide and clamped together in the channel shaped chamber holder. The empty chamber assemblies are then placed into the carrier in the bottom of the head. Finally, the samples are sequentially introduced into the chambers. Since the chamber holders tilt the chambers as above described, the samples in each chamber remain spaced from their respective slide surfaces.
The operation of loading the samples into the chambers takes a finite period of time. During this time period, the heavier cellular material suspended in each of the previously loaded fluid samples tend to sediment to the bottom of the holding portion of the sample chamber. When the samples are then centrifuged, even if the samples loaded were identical, there may be differing amounts of cellular material deposited onto the slides, depending on the amount of prior sedimentation that has taken place in each chamber. In addition there may be a nonuniform distribution of cellular material on each slide with a higher concentration toward the slide surface region adjacent the bottom of the holding portion of the chamber. These disparities and discrepancies between slides prepared from otherwise identical samples are undesirable. They are minimized by keeping the sample volumes extremely small, on the order of one millimeter or less, and minimizing the surface area of the slide which is covered by the discharge opening. In addition, care is taken to minimize the time taken to load the centrifuge sample chambers with samples prior to centrifuging. These sample size limitations can limit the cellular concentration levels which may be detected and therefore the accuracy of and time and labor required for some analyses. In addition, it would be more efficient to centrifuge a larger sample volume if it weren't for the effects of prior sedimentation during sample loading. Thus there is a need for being able to centrifuge larger sample volumes, for example, in order to detect smaller concentrations of specific biological materials. There is also a need for a method to reduce the effects of sedimentation during chamber loading and for providing a more uniform distribution of cellular material onto a microscope slide during centrifugation.
The novel method and improved large volume cytology (or cytocentrifuge) chamber in accordance with the present invention meets these needs by ensuring a more even distribution of biological material on the surface of a microscope slide during centrifugation.